1. Field of the Invention
The invention relates to a silicoaluminophosphate (SAPO) molecular sieve and to a method of producing this SAPO molecular sieve.
2. Description of Related Art
SAPO molecular sieves are used, for example, as catalyst materials in various chemical reactions. Use as a catalyst for conversion from an oxygenate to an olefin is available as one such application. SAPO-34 in particular has received attention as an important catalyst among the SAPO molecular sieves for such catalyst applications.
SAPO-34 is a SAPO molecular sieve with the CHA structure and is available exhibiting a high lower olefin selectivity in the conversion of methanol to olefin. It has been reported that SAPO-34 with a smaller crystal size exhibits a better catalytic activity (U.S. Pat. No. 5,126,308) in this reaction, and a great deal of research has been carried out into micronizing the catalyst.
A method of producing SAPO-34 having a crystal size of not more than 100 nm is disclosed in Published Japanese Translation of PCT Application No. 2005-511669 (JP 2005-511669 A). Here, SAPO-34 having a cubic-like morphology of not more than 100 nm is produced by adding ethanol to a hydrogel and carrying out hydrothermal synthesis.
It is disclosed in U.S. Pat. Nos. 6,773,688 and 7,052,664 that SAPO-34 having a crystal size of not more than 100 nm can be produced by carrying out hydrothermal synthesis after dissolving the silica source in a basic organic template solution.
The production of SAPO-34 having an average crystal size of 75 nm by carrying out hydrothermal synthesis after drying the hydrogel to give a dry gel is disclosed by Hirota, Y., et al. Materials Chemistry and Physics (2010) 123, 507-509.
Thus, as indicated above, zeolites and particularly SAPO-34 having a small crystal size can be obtained by various methods. However, an organic solvent must be used in the method of JP 2005-511669 A, which then requires the use of a reactor that exhibits greater pressure resistance than an ordinary hydrothermal synthesis apparatus. The methods in U.S. Pat. Nos. 6,773,688 and 7,052,664 and Hirota, Y., et al. Materials Chemistry and Physics (2010) 123, 507-509 require a pretreatment of the starting material, i.e., dissolution or drying, which creates the problem that a one-pot production cannot be carried out.